A revision of the Longipinnate Ichthyosaurs of the Lower Jurassic of England, with descriptions of two new species (Reptilia: Ichthyosauria)

Life Sciences Contribution 97
Royal Ontario Museum

A Revision of the Longipinnate
Ichthyosaurs of the Lower Jurassic
of England, with Descriptions of
Two New Species

(Reptilia: lchthyosauria)

C. McGowan

ROM

= ss

_ Digitized by the Internet Archive
in 2011 with funding from
_ University of Toronto

LIFE SCIENCES CONTRIBUTIONS
ROYAL ONTARIO MUSEUM

NUMBER 97

c. MccowAN A Revision of the Longipinnate
Ichthyosaurs of the Lower Jurassic
of England, with Descriptions of
Two New Species
(Reptilia: [chthyosauria)

Publication date: 29 April 1974
ISBN 0-88854-151-1
Suggested citation: Life Sci. Contr., R. Ont. Mus.

ROYAL ONTARIO MUSEUM
PUBLICATIONS IN’ LIFE ‘SCIENCES

The Royal Ontario Museum publishes three series in the Life Sciences:

LIFE SCIENCES CONTRIBUTIONS, a numbered series of original scientific publi-
cations, including monographic works.

LIFE SCIENCES OCCASIONAL PAPERS, a numbered series of original scientific
publications, primarily short and usually of taxonomic
significance.

LIFE SCIENCES MISCELLANEOUS PUBLICATIONS, an unnumbered series of
publications of varied subject matter and format.

All manuscripts considered for publication are subject to the scrutiny and
editorial policies of the Life Sciences Editorial Board, and to review by
persons outside the Museum staff who are authorities in the particular field
involved.

LIFE SCIENCES EDITORIAL BOARD

Chairman: R. L. PETERSON
Editor: D. W. BARR

Associate Editor: J. C. BARLOW
Associate Editor: J. R. TAMSITT

CHRISTOPHER MCGOWAN is Assistant Curator, Department of Vertebrate Palaeontology,
Royal Ontario Museum, and Assistant Professor, Department of Zoology, University
of Toronto.

PRICE: $1.50
© The Royal Ontario Museum, 1974
100 Queen’s Park, Toronto, Canada

PRINTED AT THE BRYANT PRESS LIMITED

A Revision of the Longipinnate
Ichthyosaurs of the Lower Jurassic of
England, with Descriptions of Two
New Species (Reptilia: [chthyosauria)

Abstract

A revision of the longipinnate ichthyosaurs of the English Lias
(Lower Jurassic) establishes five valid species. One of these
is referred to the Upper Liassic genus Stenopterygius, the
others to the genus Temnodontosaurus Lydekker, 1889, which
is predominantly Lower Liassic in age. Two new Lower Liassic
species are described. A detailed account of the variates meas-
ured is given.

Zusammenfaasung

Eine Revision der longipinnaten Ichthyosaurier des englischen
Lias (Untere Jura) stellt fuenf gueltige Arten auf. Eine von
diesen bezieht sich auf die aus dem oberen Lias stammende
Gattung Stenopterygius, die anderen auf die Gattung Temno-
dontosaurus Lydekker, 1889, welche ueberwiegend aus dem
unteren Lias stammt. Ein ausfuehrlicher Bericht ueber die
gemmessenen Verschiedenheiten wird gegeben.

Introduction

The Lower Jurassic deposits of England are well endowed with the remains
of ichthyosaurs, which have been collected intensively since the beginning
of the last century. Most material came from the Lower Lias [Hettangian and
Sinemurian], the principal localities being Lyme Regis, Dorsetshire; Street,
in the adjoining county of Somersetshire; and Barrow-on-Soar, Leicester-
shire. Ichthyosaurs are also known from the Upper Lias [Lower Toarcian],
but this horizon has so far yielded only longipinnates. The principal Upper
Liassic locality is the Whitby district of Yorkshire, equivalent in age to the
famous Holzmaden locality of Germany. Longipinnates are also found in the
Lower Lias but are less numerous than latipinnates. The distinction between
latipinnates and longipinnates is discussed in detail elsewhere (McGowan,
1972a), the major differences occurring in the forefins; longipinnates have
three distal carpals hence three primary digits, whereas latipinnates have
four distal carpals thus four primary digits.

A recent review of the Lower Liassic latipinnates (McGowan, in press)
showed the systematics to be confused, two thirds of the species being
invalid. Similar confusion occurs in the longipinnates and the problem is

|

complicated by the question of the generic name. The Luiassic latipinnates
belong to the genus Jchthyosaurus De La Beche and Conybeare, 1821, but
the appropriate name for the Liassic longipinnates is problematic. Charig
(in preparation) has made a detailed study of the nomenclatural status of
the English Liassic ichthyosaurs. He notes that as Temnodontosaurus
Lydekker, 1889 (in Nicholson and Lydekker, 1889) has I. platyodon
Conybeare, 1822, as its type-species, Temnodontosaurus is available as the
generic name for that taxon. My study shows J. platyodon to be one of a
group of four species referable to a single genus, and Temnodontosaurus
thus has priority as the generic name for these longipinnates.

As many as eight longipinnate species have been described from the
English Lias (see Lydekker, 1889a; Von Huene, 1922) and these will be
referred, for the present, to their original genus, Ichthyosaurus: I. acuti-
rostris Owen, 1840; I. crassimanus Blake, 1876; J. latifrons Koenig, 1825;
I. lonchiodon Owen, 1840; I. longifrons Owen, 1881; I. longirostris Man-
tell, 1851; J platyodon Conybeare, 1822; and I. zetlandicus Seeley, 1880.
The purpose of this paper is to clarify the systematics of these English
longipinnates.

Materials and Methods

Materials

Measurements were taken directly from 20 specimens and from photo-
graphs of an additional four specimens. Of these, 13 were from the Lower
Lias [Hettangian and Sinemurian] of Lyme Regis, Street, and Barrow-on-
Soar, and 11 from the Upper Lias [Lower Toarcian] of Whitby. The
abbreviations used for collections examined are: BMNH, British Museum
(Natural History), London; LcM, Leicester County Museum, England;
OuUM, Oxford University Museum; ROM, Royal Ontario Museum, Toronto;
scc, Street Collection, in the care of Clarks Shoe Company, Street, Somer-
set; SMC, Sedgwick Museum, Cambridge University; UW, University of
Wyoming; wmMy, Whitby Museum, Yorkshire; and yM, York Museum,

Yorkshire.

Methods

All measurements were made with
vernier calipers accurate to .01 cm,
except those of body length which
were made with a tape accurate to
0.1 cm. Because of incomplete pres-
ervation or exposure of bony ele-
ments (the term indeterminate is
used in this context in the sections
which follow ) few post-cranial char-
acters were used, viz: length of
body, vertebral count to pelvic gir-
dle, vertebral count to tail bend,
length of forefin, width of forefin,
total digital count, number of pri-
mary digits, number of accessory
digits, number of elements in long-
est digit, and occurrence of notching
(Fig. 1).

The cranial measurements re-
corded are shown in Fig. 2. Because
of size variation it was necessary to
convert all continuous variates into
ratios, and those derived from cran-
ial measurements are: diameter of
orbit (3) to length of jaw (7),
length of snout (6) to length of jaw
(7), length of premaxillary segment
(1) to length of jaw (7), length of

notches

Ci
ON Z

OO
te
O

accessory
digit
primary
digits

Fig. 1 Diagram of a longipinnate forefin
(left, dorsal view) showing the
distinction between primary and
accessory digits. The maximum
number of elements in the longest
digit is 12.

Fig. 2 Diagram of an ichthyosaur skull showing the cranial measurements:
1, length of premaxillary segment; 2, length of external naris; 3, diameter of
orbit; 4, internal diameter of sclerotic ring; 5, length of prenarial segment;
6, length of snout; 7, length of jaw.
A-A, longitudinal axis of orbit; B-B, longitudinal axis of skull; Ang, angular;
Dent, dentary; Quad, quadrate; Sur, surangular; Max, maxilla.

prenarial segment (5) to length of jaw (7), length of external naris (2) to
diameter of orbit (3), internal diameter of sclerotic ring (4) to diameter of
orbit (3). Due to small sample sizes and missing data a statistical analysis was
not possible. It is therefore not known whether the ratios are affected by
allometric growth, nor whether they are normally distributed. However,
I have found intercranial growth (relative to jaw length) to be almost
completely isometric in Stenopterygius quadriscissus, Ichthyosaurus com-
munis and I. breviceps (McGowan, 1973a) and this might also hold for
the present species. Furthermore an analysis of data for 7. communis and
I. breviceps (McGowan, in press) and S. quadriscissus (McGowan, in
preparation) has shown all ratios to be normally distributed.

Details of Variates Recorded

AXIAL SKELETON

Length of body: the length, measured along the vertebral column,
from first to last vertebra.

Vertebral count to the pelvic girdle: the number of vertebrae
counted from the atlas to the position of the pelvic girdle. The atlas is
quite distinct because it is fused with the axis (Fig. 3A). The position of
the pelvic girdle is taken as that centrum which lies closest to the vertical
level of the ilium. The pelvic girdle is frequently displaced or lost and in
this case an estimate is made based upon the position of the proximal
head of the femur.

Vertebral count to the tail bend: the number of vertebrae counted
from the atlas to the apex of the tail bend. Where the tail bend is distinct
there is little difficulty in making the count which is continued up to, and
includes, that centrum at the apex of the bend. The apical centra are

4

May

VAYAMA

(00 0o0poenoncccnnn:

constriction

Fig. 3 Features of the ichthyosaurian vertebral column, scale = 10 cm.
A. Anterior portion of vertebral column of Ichthyosaurus communis, Lower Lias,
Lyme Regis; A, atlas centrum; B, axis centrum; C, centrum of third cervical
vertebra; D, neural arch of atlas; E, neural arch of axis; F, fused neural spine
of atlas and axis; G, neural spine of third vertebra; H, neural arch of third
vertebra.
B. Tail bend region of Jchthyosaurus communis (BMNH 2013), Lower Lias,
Lyme Regis. Note the wedge-shaped centra at the apex of the bend.
c. Diagrammatic representation of the tail bend region in a dorso-ventrally
preserved specimen showing how the rate of decrease in diameter of the centra

is reduced distal to the apex of the bend.

wedge-shaped, widest dorsally, and these clearly mark the apex of the tail
bend (Fig. 3B). Where the bend is indistinct, as in dorso-ventrally com-
pressed specimens, its position can often be estimated by considering the
rate of taper in the diameter of the centra. The gradual decrease in diam-
eter towards the tip of the tail is less marked in those centra lying distal
to the tail bend than in those proximal to the tail bend. Consequently
there is a slight constriction at this level (Fig. 3c). When a constriction
is not apparent its position can often be revealed by measuring the diam-
eters of the centra, a marked difference in the diameters of adjacent centra
indicating the position of the tail bend.

SKULL (see Fig. 2)

Length of skull: the distance between the tip of the snout and the
posterior edge of the articular surface of the quadrate. The quadrate is
selected as a point of reference because it has no contact with post-cranial
structures and is therefore usually well defined. Occasionally the quadrate
is displaced, in which case allowances must be made.

Length of snout: the distance between the tip of the snout and the
anterior boundary of the orbit. Von Huene (1922) measured to the
anterior boundary of the external narial opening, but the boundaries of the
naris are often indeterminate.

Length of prenarial segment: the distance between the tip of the
snout and the anterior boundary of the external naris. Occasionally the
bones surrounding the narial aperture are pushed inwards, forming a trian-
gular depression, and this may be misinterpreted as the external naris. As a
general guide the anterior boundary of the external naris is rounded,
whereas depressions tend to be angular.

Length of premaxillary segment: the distance between the tip of
the snout and the anterior tip of the maxilla. The free margin of the maxilla
forms a continuous straight edge with that of the premaxilla, and a break in
continuity in this region is indicative of damage or displacement of the
maxilla. Where such damage has occurred an approximation can be made
by projecting the maxillary margin forward until it intersects with the
premaxilla.

Longitudinal diameter of orbit: the maximum internal diameter of
the orbit. The orbit is oval rather than round, and its longitudinal axis
may not necessarily correspond with the longitudinal axis of the skull (an
axis passing through the tip of the snout and the articular surface of the
quadrate). The longitudinal diameter of the orbit is measured along the
orbital axis, at the widest point. The posterior boundary of the orbit is
invariably well defined and is the anterior surface of the postorbital. The
anterior boundary is the internal (posterior-facing) surface of the lachry-
mal. Sometimes the lachrymal bears a posterior projection of bone which
has the appearance of a crescentic swelling in the antero-dorsal corner of
the orbit and which interferes with the measurement. However, by pro-
jecting the line of the orbit (i.e., the curvature of the jugal) forward, it
is possible to estimate the anterior boundary of the orbit.

6

Internal diameter of sclerotic ring: the maximum internal diam-
eter of the sclerotic ring. The aperture of the sclerotic ring is usually oval,
and the maximum internal diameter lies approximately parallel to the
longitudinal axis of the orbit. If distortion has occurred and the maximum
diameter lies perpendicular to the longitudinal axis of the orbit, or if the
aperture is asymmetric, a correction must be made. In both instances the
internal diameter is taken as the mean of the maximum diameter, and the
diameter measured at right angles to it.

Length of external naris: the distance between anterior and pos-
terior boundaries of the external naris measured between verticals.

LOWER JAW

Length of jaw: the distance between the anterior tip of the dentary
and the posterior edge of the surangular, measured between verticals
perpendicular to the longitudinal axis of the skull.

DENTITION

Form of teeth: the teeth lie with their bases in a dentigerous groove
and for this reason are seldom seen in their entirety. Note is taken of the
tooth shape.

Number of maxillary teeth: the number of teeth in the upper jaw
counted from the most posterior tooth, to that at the anterior tip of the
maxilla. The most anterior maxillary tooth may lie partly in contact with
the premaxilla, but provided it maintains contact with the maxilla it is
counted as a maxillary tooth.

FINS (see Fig. 1)

Length of fore- and hindfin: the distance between the distal end of
the propodial and the most distal phalanx, measured between horizontals
perpendicular to the longitudinal axis of the fin. The propodial is not
included in the length of the fin because of the difficulty in accurately deter-
mining its length. The terminal phalanges are usually very small and often
well spaced so that they do not make contact with one another. Sometimes
they are obscured by matrix, or lost altogether, but if the most distal
phalanges are relatively small it may be assumed that the fin is complete.

Width of fore- and hindfin: the maximum width measured between
verticals parallel to the longitudinal axis of the fin.

Number of primary digits: the maximum number of primary digits.

Total digital count: the total number of primary and accessory
digits. Accessory digits frequently contain only a few elements, but if they
exceed three in number they are counted.

Occurrence of notching in fin elements: notches are often obscured
by matrix, which it is sometimes necessary to remove.

Number of elements in longest digit: numerically equal to the
horizontal level of the most distal fin element. The count commences at
the level of the epipodials (level one).

Estimates of Growth Constants a and b

Estimates of the allometric growth constants a@ and b for the growth of
the head relative to the body were evaluated using the logarithmic trans-
formation of the allometric growth equation y = bx® (where y = organ
size and x = body size). Bartlett’s Model I! regression technique was used
in the computation, but the small sample size did not permit confidence
limits to be set for the estimates of a and b (for details of the method see
McGowan, 1973a).

Systematic Descriptions

I find that only three of the eight previously described English longipinnate
species from the Lower Jurassic are valid; /. platyodon Conybeare, I.
acutirostris Owen and I. longirostris Mantell. To these three are added
two new species (described below), both from the Lower Lias of Lyme
Regis, Dorset. J. crassimanus Blake, I. longifrons Owen and I. zetlandicus
Seeley are all junior synonyms for J. acutirostris; I. lonchiodon Owen is a
junior synonym for J. platyodon, and I. latifrons Koenig is rejected as a
nomen dubium.

I. acutirostris (Upper Lias, Yorkshire) has closer affinity with the Ger-
man species Stenopterygius quadriscissus (Quenstedt) (Upper Lias) than
with the other English longipinnates, and is accordingly referred to the
genus Stenopterygius. The remaining four English species are referred to
the genus Temnodontosaurus Lydekker (1889b, pp. xi, 1126).

Class Reptilia

Subclass Euryapsida(?)

Order Ichthyosauria

Suborder Longipinnati Von Huene, 1948

Family Temnodontosauridae fam. nov.

Diagnosis

Forefin with no more than three primary digits, one of which supported
by intermedium; total digital count probably does not exceed four; orbit
relatively small, ratio, diameter of orbit to length of jaw < 0.21; aperture
of sclerotic ring to diameter of orbit probably always < 0.35; maxilla
relatively long, ratio, length of premaxillary segment to length of jaw
< 0.40; external naris frequently relatively long, ratio, length of external
naris to diameter of orbit often > 0.45; moderate to very large, adult jaw
length > 60 cm and usually > 100 cm. Liassic in age and predominantly
from the Lower division.

Type genus 7emnodontosaurus Lydekker 1889b
Diagnosis
As for the Family Temnodontosauridae

Type species
Temnodontosaurus platyodon (Conybeare)

Fig. 4 Temnodontosaurus platyodon (Conybeare), scale = 25 cm.
A. BMNH 2003, dorsal view, Lower Lias, Lyme Regis; B. BMNH R1158, Lower
Lias, Lyme Regis; C. BMNH 2003, left forefin, dorsal view; D. oUM J29170, right
forefin, ventral view, Lower Lias, Lyme Regis.

10

Temnodontosaurus platyodon (Conybeare)
Fig. 4

Ichthyosaurus platyodon Conybeare, 1822, p. 108, pl. 15, fig. 7; pl. 16,
figs. 1-7.

Ichthyosaurus platyodon Conybeare, De La Beche, 1826, p. 27.
Ichthyosaurus chiroligostinus Hawkins, 1834, p. 14, pl. 3.

Ichthyosaurus chiroligostinus Hawkins, Hawkins, 1840, p. 10, pl. 2, pl. 3.
Ichthyosaurus platyodon Conybeare, Owen, 1840, p. 112.

Ichthyosaurus lonchiodon Owen, 1840, p. 116.

Ichthyosaurus platyodon Conybeare, Mantell, 1851, p. 380.

Ichthyosaurus lonchiodon Owen, Mantell, 1851, p. 384.

Ichthyosaurus platyodon Conybeare, Owen, 1881, p. 115, pl. 24, fig. 4;
pl. 31, figs. 1-3.

Ichthyosaurus lonchiodon Owen, Owen, 1881, p. 117, pl. 24, fig. 6; pl. 31,
figs. 4-7.

Ichthyosaurus platyodon Conybeare, Lydekker, 1889a, p. 94, fig. 34.
Ichthyosaurus lonchiodon Owen, Lydekker, 1889a, p. 92.
Temnodontosaurus platyodon (Conybeare), Lydekker, 1889b, p. xi.
Leptopterygius platyodon (Conybeare), Von Huene, 1922, p. 18, pl. 2,
figs 2. pl.3: fig: 3.

Leptopterygius lonchiodon (Owen), Von Huene, 1922, p. 16, pl. 3, fig. 1.
Leptopterygius (Ichthyosaurus) platyodon (Conybeare), Delair, 1969, p. 10.
Leptopterygius platyodon (Conybeare), Delair, 1969, p. 11.

Proteosaurus platyodon (Conybeare), McGowan, 1972a, p. 5, fig. 2b.
Proteosaurus platyodon (Conybeare), McGowan, 1972b, p. 5, figs. 9, 11.

Emended Diagnosis

Very large ichthyosaurs, length of jaw > 100 cm, and > 150 cm in mature
individuals; snout relatively long and straight, ratio, length of snout to
length of jaw > 0.62; skull and lower jaw with rectilinear profile; orbit
relatively small, ratio, diameter of orbit to length of jaw not exceeding 0.18
and probably always < 0.18; sclerotic aperture relatively small, ratio,
internal diameter of sclerotic ring to diameter of orbit < 0.35; maxilla
relatively long, ratio, length of premaxillary segment to length of jaw
< 0.36; external naris relatively long, ratio, length of external naris to
diameter of orbit usually > 0.60; ratio, length of prenarial segment to
length of jaw > 0.42; forefin long and narrow with three primary digits
and probably one post-axial accessory digit; maximum number of elements
in longest digit does not exceed 18; radius and radiale notched, possibly
other elements too. Lower Liassic in age [Upper Hettangian to Lower
Sinemurian] and largely, if not wholly, confined to Lyme Regis, Dorset-
shire.

Original type material
A single tooth was figured in the original description of the species /. platy-
odon (Conybeare, 1822, pl. 15, fig. 7), which was in the care of the Geolog-

vd

ical Society of London (Woodward and Sherborn, 1890, p. 240). A search
for this tooth was unsuccessful (Delair, 1960).

Proposed Neotype
BMNH 2003, a complete skeleton in the British Museum (Natural History).

Evidence that proposed neotype is consistent with what is known of original
type material

Conybeare’s original description of J. platyodon made reference to the large
size, “the most gigantic yet discovered” (1822, p. 108). The proposed neo-
type, BMNH 2003, with a total length of 6.38 metres, is one of the largest
Lower Liassic specimens, and is therefore consistent with Conybeare’s
original description.

Evidence that proposed neotype came as nearly as practicable from original
type-locality

Conybeare did not specify the type-locality but did note that the species
occurred in the Lias (1822, p. 108). At that time most ichthyosaurian
material was being collected from Lyme Regis, and to a lesser extent from
Somerset. As both of these localities are Lower Liassic, it may be inferred
that the material was Lower Liassic in age.

Other material

BMNH R2918, BMNH 14564 (complete skeletons); ouM J29170 (incom-
plete skeleton); BMNH R1158, BMNH R1155, BMNH R215 (complete or
near complete skulls) and RoM 7972 (partial skull).

Locality and Horizon

All material thus far referred to this species is from the Lower Lias of
Lyme Regis, Dorset. De La Beche (1822) noted that remains of ichthy-
osaurs were “by no means rare” and were principally discovered at Black
Ven, most commonly in the slaty or marly part of the Lias. The lowest
horizon exposed at the foot of Black Ven is that of Arnioceras semi-
costatum (Fig. 5). In a later paper De La Beche (1826) recorded that
the Liassic limestones of Lyme Regis contain numerous organic remains,
including ichthyosaurs, which are found principally in the marls alternating
with limestones containing the ammonite, Arietites bucklandi (i.e., the top
of the Blue Lias). Most of the material from Lyme Regis was probably
collected from the Blue Lias, from the zones of Arietites bucklandi and
Arnioceras semicostatum (see Arkell, 1933). While it is possible that ich-
thyosaurs have been collected from higher zones, the geological range of
specimens from Lyme Regis will be taken to be from the zone of Schlo-
theimia angulata to that of Arnioceras semicostatum [Upper Hettangian—
Lower Sinemurian].

Emended Description
Temnodontosaurus platyodon is one of the largest ichthyosaurs, second
only to Cymbospondylus petrinus (Middle Traissic, Nevada) in total body

12

LITHOLOGICAL
STAGES ZONES FORMATIONS LOCALITIES

raricostatum

Echioceras

Black Marl of
Black Ven

Shales-with- Beef”
Arietites bucklandi
Schlotheimia angulata Blue Lias

Alsatites liasicus

Oxynoticeras oxynotum

Lyme Regis

Asteroceras obtusum

Dorset

Caenisites turneri

SINEMURIAN

Arnioceras semicostatum

HET TANGIAN

Street
Somerset

Fig. 5 The ammonite zones of the English Lower Lias (based upon Dean et al., 1961).

Psiloceras planorobis

length. C. petrinus has been estimated to reach 10 metres (McGowan,
1972b), whereas T. platyodon probably did not exceed 9 metres (data from
BMNH R1155 and BMNH 2003).

SKULL

Snout relatively long and straight, tapering gently to the tip. Ratio, length
of snout to length of jaw 0.64 in neotype, observed range 0.62—0.64
(n = 3). Maxilla long and robust, makes substantial contribution to mar-
gin of upper jaw; ratio, length of premaxillary segment to length of jaw
0.34 in neotype, observed range 0.30—-0.34 (n = 2). As noted elsewhere
(McGowan, 1972a), possession of a relatively long maxilla is a primitive
character.

Orbit relatively small; ratio, diameter of orbit to length of jaw 0.16 in
the neotype, observed range 0.16—0.17 (n = 3). Sclerotic aperture also
relatively small; ratio, internal diameter of sclerotic ring to diameter of
orbit (indeterminate in neotype) 0.32 in ROM 7972, 0.31 in BMNH R1158
and 0.24 in BMNH R215. Possession of small orbital and sclerotic diam-
eters are both primitive characters (McGowan, 1972a). External naris
large; ratio, length of external naris to diameter of orbit, probably always
exceeding 0.50, is 0.53 in ROM 7972, 0.63 in BMNH R1158 and BMNH
R1155, and 0.72 in BMNH R215. Ratio, length of prenarial segment to
length of jaw 0.50 in neotype, range 0.46-0.50 (n = 3). Naris bilobed
in BMNH R1158 (Fig. 6B), but not bilobed in either RoM 7972 or BMNH
14564 and not therefore a constant character. External lateral surfaces of
tips of premaxillae marked in neotype (Fig. 6A) by fairly deep longitudinal
striations, which converge anterodorsally giving serrated medial margin.

Es

aoe

wot Fe
sects
PIO rae

eoore
od ete headed ed

Fig. 6 Temnodontosaurus platyodon (Conybeare), scale = 5 cm.
A. BMNH 2003, tip of snout, dorsal view, showing striations.
B. BMNH R1158, external naris, lateral view, showing bilobed appearance.

14

Because extreme tip of snout frequently lost in other specimens, it is not
known if this is a diagnostic character. Internasal foramen (McGowan,
1973b) present in neotype, BMNH R1155, BMNH R215, and ROM 7972, but
absent in BMNH R1158 and indeterminate in remaining specimens; may be
considered a constant character. |

Probably also to be referred to T. platyodon are BMNH 2149 (and BMNH
2150), a basioccipital and basisphenoid with associated atlas and axis, and
BMNH 481, a partial vertebral column. Both specimens are from the Lower
Lias of Lyme Regis, and are large (dorso-ventral height of centra 18.5 cm,
width of basisphenoid 24.7 cm). It is noteworthy that the basioccipital is
not drawn out into a peg anteriorly, as in latipinnates (McGowan, 1973b)
but has a flat anterior face. A similar basioccipital condition occurs in the
Cretaceous longipinnate Platypterygius americanus (UW 2421), and in an
undescribed longipinnate skull from the Upper Jurassic of Norfolk (smc
J68516). It is suggested that the absence of a basioccipital peg may be a
longipinnate character.

FINS

Whereas the skull of T. platyodon is adequately known, knowledge of fin
structure is incomplete because of scarcity of associated skeletons. Fore-
and hindfins both preserved in neotype, but close inspection reveals right
forefin is entirely plaster, and last two (distal) horizontal rows of left hind-
fin are plaster also. From level six onwards (radius and ulna are designated
level one, radiale, intermedium and ulnare level two, and so on; see
“Materials and Methods”) elements of left forefin well spaced, giving sus-
piciously unnatural appearance. However, all elements are embedded in
matrix (which has been painted) and there is even a small depression
indicating where an element has been lost (distal to level 8); left forefin
therefore genuine. Bones of two hindfins similarly embedded in matrix and
likewise reliable.

In neotype hindfin approaches size of forefin; ratio, forefin length to hind-
fin length 1.4 (mean value 2.5 in Stenopterygius quadriscissus). Both fins long
and narrow; aspect ratio (maximum length/maximum width) of left forefin
3.4 (mean value 2.3 in S. quadriscissus). Aspect ratio of left and right
hindfins 2.6 and 2.2 respectively (mean value 2.1 in S. quadriscissus).
Three primary digits in neotype forefin with evidence of a pre-axial
accessory digit commencing at level eight; as this consists of only two
elements it can be ignored. Maximum number of elements in the longest digit
16. Notching in first three pre-axial elements. Forefins incomplete in BMNH
R2918 but have three primary digits, one post-axial accessory. Longest
digit has 12 elements, but incomplete. In oumM J29170 right forefin more
complete than left, has three primary and one accessory digits. Maximum
number of elements in longest digit 14; radius and radiale notched.

In conclusion, the forefin has three primary digits and one post-axial
accessory digit, the maximum number of elements in the longest digit
probably does not exceed 18, and the radius and radiale are notched. The
hindfin (in the neotype) has three primary and one post-axial accessory

HS)

Fig. 7 A comparison of the pectoral girdle of BMNH 2003 and BMNH 14564 (after
Owen, 1881).
Cl, clavicle; Co, coracoid; H, humerus; Sc, scapula; Ant n, anterior notch.
A. BMNH 2003, Lower Lias, Lyme Regis (pl. 31, fig. 3). [7. platyodon]
B. BMNH 14564, Lower Lias, Lyme Regis (pl. 31, fig. 4). [J. lonchiodon]

digits, and the maximum number of elements in the longest digit is 12. The
forefin is only marginally longer than the hind, and has a high aspect ratio.

AXIAL SKELETON AND GIRDLES

Vertebral count from atlas to pelvic girdle 46 or 47 in neotype, estimated
46 in BMNH R2918, and 46 or 47 in BMNH 14564. Only in BMNH R2918
is vertebral column sufficiently well preserved for a vertebral count to the
tail bend, estimated at 86 or 87 (mean counts to pelvic girdle and tail
bend 47 and 83 respectively in S. quadriscissus, and 44 and 77 in the
latipinnate [chthyosaurus communis). Pre-flexural body segment relatively
longer in 7. platyodon than S. quadriscissus (see McGowan, 1972b, Fig.
17); T. platyodon was a longer-bodied animal. Individual vertebral centra
with typical ichthyosaurian disc shape; in neotype (jaw length 148 cm)
diameter of dorsal centra 11.5 cm, in ouM J29170 (jaw length 169 cm),
dorsal centra 14.5 cm. In longest skull recorded, BMNH R1155 (jaw length
approximately 221 cm), cervical centra 13.5 cm diameter compared with
18.5 cm in partial vertebral column BMNH 481. It is therefore concluded that
the length of the jaw may have exceeded 221 cm. The limb girdles are in-
variably indeterminate in ichthyosaurs, and thus of reduced systematic inter-
est, but it may be noted that they are relatively large and robust in T. platy-
odon. The coracoid apparently has only an anterior notch (Fig. 7B: Ant n).

DENTITION

Teeth are of little value in ichthyosaur classification (McGowan, 1969)
and it is interesting to note that Conybeare’s flattened “platyodon tooth”
(Conybeare, 1822, pl. 15, fig. 7) is absent from all specimens thus far

16

referred to the species 7. platyodon (and for that matter from other
ichthyosaurs examined). Teeth are clearly visible in the neotype (BMNH
2003), BMNH R1158, BMNH R215, and RoM 7972 and all are round in
cross-section.

Remarks

Figures were not given by Owen in his description of J. lonchiodon, but
reference was made to a specimen 15 feet (4.5 metres) long in the British
Museum (BMNH 14564) purchased from T. Hawkins and figured in a
subsequent paper (Owen, 1881, pl. 31, figs. 4-7). In his original descrip-
tion Owen compared I. lonchiodon with I. platyodon noting the following
differences: head of J. lonchiodon relatively longer, lower jaw deeper and
tapering more rapidly to tip, teeth more slender with circular cross-section,
vertebral centra wider antero-posteriorly, scapula with deeper posterior
concavity, forefin relatively smaller and fore-and hindfins do not approach
similar size as they do in J. platyodon. Owen referred BMNH 2003 and
BMNH R1158 to J. platyodon (1881, pl. 31, figs. 1 and 2 respectively),
but if these specimens are compared with the holotype of J. lonchiodon
(BMNH 14564) they are found to be indistinguishable on Owen’s diag-
nostic characters:

BMNH 2003 BMNH RI158 BMNH 14564

Length of skull
ee 0.28 — 0.28
Length of body
Depth of jaw
—— — 0.10 0.10
Length of jaw
Shape of tooth section Round Round ——
Width of centrum

0.40 — 0.38

Height of centrum (30th centrum)

Furthermore, if the scapula of BMNH 2003 is compared with that of BMNH
14564 (Owen, 1881, pl. 31, figs. 3-4), it is seen that while they differ some-
what in shape, the posterior concavity is no deeper in BMNH 2003 (Fig. 7).
The species J. lonchiodon Owen is thus concluded to be a junior synonym
for T. platyodon (Conybeare).

Temnodontosaurus risor sp. nov.
Fig. 8

Etymology
Risor, Latin (masc.), a mocker

Ichthyosaurus communis Conybeare, Owen (pro-parte), 1840, p. 108.
Ichthyosaurus communis Conybeare, Lydekker (pro-parte), 1889a, p. 41,
fig. 21.

17

EE

Fig. 8 Temnodontosaurus risor sp. nov., scale = 25 cm.
A. BMNH 43971, holotype, Lower Lias, Lyme Regis.
B. SMC J68446, Lower Lias, Lyme Regis.
C. BMNH R311, Lower Lias, Lyme Regis.

18

Diagnosis

Medium sized ichthyosaurs, length of jaw < 100 cm; snout distinctly re-
curved, ratio, length of snout to length of jaw > 0.57 but probably not
exceeding 0.62; skull and lower jaw with recurved profile; orbit relatively
large, ratio, diameter of orbit to length of jaw > 0.18; sclerotic aperture
relatively small, ratio, internal diameter of sclerotic ring to diameter of
orbit < 0.35; maxilla of moderate length, ratio, length of premaxillary
segment to length of jaw > 0.36; ratio, length of prenarial segment to
length of jaw > 0.42; maxillary tooth count > 15. Lower Liassic in age
[Upper Hettangian to Lower Sinemurian]; largely, if not wholly, confined
to Lyme Regis, Dorsetshire.

Holotype
BMNH 43971, a complete skull in the British Museum (Natural History).

Other Material
SMC J68446 (complete skull) ; BMNH R311 (partial skull).

Locality and Horizon

All material thus far referred to this species is from the Lower Lias of
Lyme Regis, Dorset. The geological range is taken to be from the zone of
Schlotheimia angulata to that of Arnioceras semicostatum (see Fig. 5)
[Upper Hettangian to Lower Sinemurian].

Description

The present species is known only from cranial material. The holotype,
a well preserved laterally compressed skull, exposed on the right, has a
jaw length of 70 cm, and is the smallest of the three referred specimens;
BMNH R311, the largest, has a jaw length of 83 cm. Characteristic of the
species is the recurved snout which imparts the sardonic expression re-
flected in the trivial name. Ratio, length of snout to length of jaw 0.59 in
holotype, observed range 0.59-0.62 (n= 3), (0.62-0.64 in T. platy-
odon, n = 3). Orbit relatively large, ratio, diameter of orbit to length of
jaw 0.20 in the holotype, observed range 0.19-0.20 (n= 3), (0.16—
0.17 in T. platyodon, n = 3). Sclerotic ring well preserved only in holo-
type; ratio, internal diameter of sclerotic ring to diameter of orbit 0.26
(0.24—-0.31 in T. platyodon, n= 4). Relative small size of maxilla re-
flected in large value of ratio, length of premaxillary segment to length of
jaw, 0.39 in holotype, range 0.38-0.39 (n = 3), (0.30—-0.34 in T.
platyodon, n = 2). Because of distortion external naris in holotype difficult
to delimit; in BMNH R311 it is relatively small, ratio, length of external naris
to diameter of orbit 0.44 (0.53-0.72 in JT. platyodon, n = 4). Ratio,
length of prenarial segment to length of jaw 0.44 in holotype, observed
range 0.44—0.49 (n = 3), (0.46—0.50 in T. platyodon, n = 3).

Remarks
T. risor is most closely related to T. platyodon, but is a much smaller
species (observed size ranges, based on jaw length, 70-83 cm and 135-

i?

221 cm respectively). In marked contrast to T. platyodon, the snout of
T. risor has a curved profile and also appears to be relatively shorter. In
possessing a relatively larger orbit and smaller maxilla than T. platyodon,
I. risor represents a more advanced stage of cranial evolution (for a dis-
cussion of evolutionary trends see McGowan, 1972a and 1972b).

The superficial resemblance to J. communis is due to their similar snout
proportions; the mean value for the ratio, length of snout to length of jaw
is 0.61 in T. risor and 0.63 in J. communis. The differences between the
two species are fundamental:

TD. risor I. communis
Diameter of orbit/length of jaw <10:71 > 0.21
Internal diameter of sclerotic ring/diameter of orbit << 0:35 > 0:35
Length of premaxillary segment/length of jaw < 0.40 > 0.40

Furthermore, 7. risor is a considerably larger species, having an observed
size range of 70-83 cm (jaw length) whereas the largest recorded speci-
men of J. communis has a jaw length of only 54 cm.

Temnodontosaurus eurycephalus sp. nov.
Fig. 9

Etymology
evpvo Gk. (masc.) wide; xedadrn Gk. (fem.) head

Ichthyosaurus breviceps Owen (pro-parte), 1881, p. 109, pl. 29, fig. 1.
[non] Ichthyosaurus platyodon Conybeare, Lydekker, 1889a, p. 98.
Eurypterygius breviceps (Owen), Von Huene, 1922, p. 8, pl. 1, fig. 3
[referred to in the figure legend, in error, as Eurypterygius brevirostris
(Owen) ].

Diagnosis

Large ichthyosaurs, adult jaw length exceeding 100 cm; snout relatively
short, ratio, length of snout to length of jaw < 0.58; skull and lower jaw
deep; orbit relatively small, ratio, diameter of orbit to length of jaw
< 0.21; ratio, internal diameter of sclerotic ring to diameter of orbit
< 0.35; maxilla relatively long, ratio, length of premaxillary segment to
length of jaw < 0.36 and probably < 0.30; external naris relatively short,
ratio, length of external naris to diameter of orbit <0.50; ratio, length of
prenarial segment to length of jaw < 0.42; teeth relatively few in number,
maxillary tooth count probably <15. Lower Liassic in age [Upper Het-
tangian to Lower Sinemurian] and largely if not wholly confined to Lyme
Regis, Dorsetshire.

Holotype
BMNH R1157, an isolated skull in the British Museum (Natural History).

Other Material
Nil
20

es mt ste —

Fig. 9 Temnodontosaurus eurycephalus sp. nov., BMNH R1157, holotype, Lower Lias,
Lyme Regis, scale = 50 cm.

Locality and Horizon

The holotype, from the Lower Lias of Lyme Regis, was collected from a
limestone bed called Broad Ledge. Broad Ledge is probably synonymous
with Grey Ledge (Woodward and Ussher, 1911, p. 37), being the top of
a platform of rocks exposed at low tide some distance from the eastern
jetty, southeast of Church Cliffs. The horizon corresponds with the zone
of Arietites bucklandi and is lowermost Sinemurian (see Fig. 5).

Description

The holotype is a large laterally compressed skull, right side exposed.
Length of lower jaw 111 cm, skull 102 cm. Snout much abbreviated, skull
roof slopes quite steeply towards tip of snout. Ratio, length of snout to
length of jaw 0.55 (0.62—0.64 in T. platyodon, n = 3). Skull and lower
jaw both very deep dorsoventrally, giving head a robust appearance. Orbit
and aperture of sclerotic ring both relatively small; ratio, diameter of orbit
to length of jaw 0.18 (0.16—-0.17 in T. platyodon, n = 3), ratio, internal
diameter of sclerotic ring to diameter of orbit 0.29 (0.24—0.31 in T.
platyodon, n= 4). Maxilla long and fairly stout, ratio, length of pre-
maxillary segment to length of jaw only 0.27 (0.30—-0.34 in T. platyodon,
n = 2). External naris set well forward and relatively small; ratio, length
of external naris to diameter of orbit 0.44 (0.53-0.72 in T. platyodon,
n = 4); length of prenarial segment to length of jaw only 0.38 (0.46—
0.50 in 7. platyodon;n = 3).

Dentition

Teeth, large conical pegs with bulbous roots, few in number, and well
spaced. The stout teeth, massive lower jaw, and broad rostrum are all
indicative of an effective crushing apparatus. T. eurycephalus may have

21

preyed upon other ichthyosaurs: the bony element (basisphenoid) clenched
between the teeth of BMNH R1157 may not be part of its own skull but that
of some victim.

Remarks

BMNH R1157 was figured and described by Owen in 1881 and referred to the
new species [chthyosaurus breviceps, even though there was a considerable
size disparity between this specimen (jaw length 111 cm) and the holotype of
I. breviceps, BMNH 43006 (jaw length 25.3 cm). The only similarity between
the two is in the extreme brevity of the snout; the ratio, length of snout to
length of jaw is 0.55 in BMNH R1157 and in BMNH 43006. However, the
orbit is much smaller in BMNH R1157, and the ratio, diameter of orbit to
length of jaw is only 0.18 compared with 0.31 in BMNH 43006. This dis-
crepancy cannot be reconciled in terms of relative growth because the
growth of the orbit appears to have had a positive allometry in J. breviceps
(McGowan, 1973a). The maxilla is relatively longer in BMNH R1157 than
in BMNH 43006, with values for the ratio, length of premaxillary segment
to length of jaw 0.27 and 0.44 respectively. Here again the disparity cannot
be explained in terms of relative growth because the maxilla appears to
have had a negative allometry in J. breviceps, larger individuals tending to
have relatively smaller maxillae (McGowan, 1973a). Possession of small
orbit, small sclerotic ring diameter and large maxilla are all longipinnate
characters (McGowan, 1972a), and there can be no doubt that BMNH R1157
is a longipinnate. BMNH R1157 cannot therefore be referred to the latipinnate
species I. breviceps, and is accordingly described here as a new longipinnate
species.

Temnodontosaurus longirostris (Mantel])
Fig. 10

Ichthyosaurus longirostris Mantell, 1851, p. 385.

[non] Ichthyosaurus longirostris Mantell, Jager, 1856, p. 951, pl. 30.
Ichthyosaurus longirostris Mantell, Owen, 1881, p. 124, pl. 25, fig. 2;
pl. 26, tis. 3; pl. 32; figs! 7;.8,-9:

Ichthyosaurus latifrons Koenig, Lydekker, 1889a, pp. 89-92, figs. 31-32.
Ichthyosaurus longirostris Mantell, Fraas, 1891, p. 63.

Leptopterygius laitfrons (Koenig), Von Huene (pro-parte), 1922, p. 15,
pl. 3, fig. 2:

Emended Diagnosis

An inadequately known species of moderate size, length of jaw probably
not exceeding 100 cm; snout very long and thin, ratio, length of snout to
length of jaw > 0.70; orbit relatively small, ratio, diameter of orbit to
length of jaw probably < 0.18; sclerotic aperture relatively large for a
longipinnate, but ratio, internal diameter of sclerotic ring to diameter of
orbit probably always < 0.35; forefin long and narrow with three primary
digits and one post-axial accessory digit; radius notched, perhaps also

22

Fig. 10 Temnodontosaurus longirostris (Mantell), scale = 50 cm.
A. BMNH 36182, Lower Lias, Barrow-on-Soar, Leicestershire, after Owen,
pl. 32, fig. 7; B. scc 1, Lower Lias, Street, Somersetshire.

1881,

radiale and other elements in first digit; maximum number of elements in
longest digit probably < 18. Liassic in age, probably ranging from Lower
to Upper divisions.

Holotype

BMNH 14566, an incomplete skeleton (dorsal aspect exposed) apparently
from the Upper Lias of Whitby, Yorkshire, figured in Owen, 1881, pl. 32,
fig. 8.

Referred Material

BMNH 36182, an almost complete skeleton from the Lower Lias of
Barrow-on-Soar; scc 1, the anterior portion of an imperfect skeleton com-
prising partial skull, near-complete forefin, and an imperfect pectoral
girdle, from the Lower Lias of Street, Somerset. BMNH R1120, a poorly
preserved skeleton from the Lower Lias of Lyme Regis figured by Owen
(1881, pl. 32; fie. 1) is also referred to the present:species:

Locality and Horizon
According to Lydekker (1889a, p. 91) the holotype is from the Upper
Lias of Whitby, Yorkshire, whereas the two referred specimens, BMNH
36182 and scc 1 are both from the Lower Lias of Barrow-on-Soar,
Leicestershire, and Street, Somerset, respectively. As far as I am aware,
no Liassic species extends from Lower to Upper divisions, but this may
be an artifact of the geological record, due to lack of good Upper Liassic
exposures (ichthyosaurs with very extensive geological ranges are known
from the Cretaceous, McGowan, 1972c). It could be that Lydekker was
mistaken in referring BMNH 14566 to the Upper Lias of Whitby; the Lower
Lias does outcrop in Whitby, but most if not all ichthyosaurs from Whitby
have been collected from the Upper Lias. For the present the geological
range of 7. longirostris is taken to extend from Lower to Upper Lias.
Most of the reptilian remains from Street have been collected from the
“pre-planorbis Beds” (Arkell, 1933, p. 123) which are at the base of the
Lower Lias [Lowermost Hettangian]. At Whitby ichthyosaurs have been
collected from the zones of Hildoceras bifrons and Harpoceras falcifer
(Hemingway et al., 1968) which are in the lower part of the Upper Lias
[Lower Toarcian]. The geological range of T. longirostris is therefore taken
to be from Lower Hettangian to Lower Toarcian.

Emended Description
Because of incomplete material, Temnodontosaurus longirostris (Mantell)
is only moderately well known.

SKULL

Snout long and thin, ratio, length of snout to length of jaw approximately
0.79 in holotype, compared with 0.72—0.73 (n = 2) in the other English
long-snouted species Ichthyosaurus tenuirostris (0.62—0.64 in T. platy-
odon, n = 3). Orbit appears large but ratio, diameter of orbit to length
of jaw only 0.16 in holotype and BMNH R1120, compared with 0.22 in
I. tenuirostris (n = 1) and 0.16-0.17 in T. platyodon (n = 3). Sclerotic

24

aperture also relatively small, ratio, internal diameter of sclerotic ring to
diameter of orbit 0.33 in holotype and scc 1, compared with 0.41 in J.
tenuirostris (n = 1) and 0.24—-0.31 in T. platyodon (n= 4).

FINS

Knowledge of the forefin is incomplete, but it is certainly longipinnate, with
three primary digits and one post-axial accessory digit (Fig. 10). The best
known forefin (scc 1) is almost complete and has a maximum number of
16 elements in the longest digit, though one or two may be missing from
the extreme tip. Only the radius is notched in scc 1 whereas in BMNH 36182
and BMNH R1120 the radius, radiale, and third element of the first digit
are emarginated. The hindfin of BMNH 36182 has three primary digits and
several of the elements of the first digit are emarginated.

Remarks

The species /. longirostris is usually attributed to Owen, 1881 (Lydekker,
1889a, p. 89; Woodward and Sherborn, 1890, p. 239; Kuhn, 1934, p. 55)
and sometimes to Jager 1856 (Lydekker, 1889a, p. 89) but the first
description of the species was given by Mantell in 1851, who wrote,
“ICHTHYOSAURUS LONGIROSTRIS Wall-case E—In...Case E
there is part of the skeleton of an Ichthyosaurus from Whitby, about six
feet [1.8 m] in length. It is remarkable for the exceedingly slender and
elongated muzzle; the skull is crushed; and with the exception of the chain
of vertebrae which extends to the tail, and a few bones of one paddle,
there are no characteristic parts preserved. The specific name, longirostris,
is affixed to this specimen; but I cannot ascertain that it is figured or
described.” (Mantell, 1851, p. 385). Sufficient information is given to
identify the specimen, the locality is recorded and, most important, note
is taken of the extremely long snout. In my opinion this constitutes a valid
description. Lydekker (1889a, p. 91) identified Mantell’s specimen as
BMNH 14566, from the Upper Lias of Whitby, and gave a description
which matches Mantell’s description, noting that the dorsal aspect of the
skull is figured by Owen (1881, pl. 32, fig. 8). Jager (1856, p. 951) did
not consider that Mantell had adequately described the species and there-
fore gave his own description which included the figure of a skull (Jager,
1856, pl. 30). This skull, however, should probably be referred to the
genus Eurhinosaurus. The skeleton figured by Fraas (1891, pl. 12, fig. 5)
from the Upper Lias of Holzmaden might be referable to T. longirostris.

25

Systematic Summary

The genus Temnodontosaurus, which is largely confined to the Lower Luias,
contains four species, 7. platyodon (Conybeare), T. longirostris (Man-
tell), and the two new species JT. risor and T. eurycephalus.

Still to be considered is J. acutirostris Owen, from the Upper Lias of
Whitby, Yorkshire. J. acutirostris and Stenopterygius quadriscissus (Quen-
stedt) [Upper Lias, Germany] are found to be almost indistinguishable
from each other but quite distinct from 7. platyodon (Table 1). I. acuti-
rostris is accordingly referred to the genus Stenopterygius. Because the
present work is confined to English material it is not appropriate to give
here an emended diagnosis of the family Stenopterygiidae, which is known
largely from Germany. This will be the subject of another study (Mc-
Gowan, in preparation).

Table 1. Comparison of cranial and body characters between the longipinnate species
S. acutirostris, S. quadriscissus and T. platyodon.

S. acutirostris
S. quadriscissus

T. platyodon

=
OD
N

“Length of snout/length of jaw
*Diameter of orbit/length of jaw

*Length of premaxillary segment/
length of jaw

*Internal diameter of sclerotic ring/
diameter of orbit

“Length of prenarial segment/
length of jaw

*Tength of external naris/
diameter of orbit

Number of primary digits

Number of accessory digits

Maximum number of elements in
longest digit

Maximum recorded size (jaw length, cm)

* Mean values

26

Family Stenopterygiidae Von Huene 1948
Genus Stenopterygius Jaekel 1904

Stenopterygius acutirostris (Owen)
Fig, 11

Ichthyosaurus acutirostris Owen, 1840, p. 121.

Ichthyosaurus longipennis Mantell, 1851, p. 378.

Ichthyosaurus acutirostris Owen, Phillips, 1875, p. 272.

Ichthyosaurus acutirostris Owen, Blake, 1876, p. 253.

Ichthyosaurus crassimanus Blake, 1876, p. 253, pl. 1, fig. 9.

Ichthyosaurus zetlandicus Seeley, 1880, pp. 635-646, pl. 25.

Ichthyosaurus acutirostris Owen, Owen, 1881, p. 121, pl. 28, fig. 2.
Ichthyosaurus longifrons Owen, 1881, p. 118, pl. 23, figs. 1-5; pl. 24,
figeie pl. 25, mele pk 26, fie. 1; pl.27, figs. 2-5.

Ichthyosaurus acutirostris Owen, Lydekker, 1889a, p. 73.

Leptopterygius acutirostris Owen, Von Huene (pro-parte), 1922, p. 25.
[non] Ichthyosaurus (cf.) acutirostris Owen, Lydekker, 1889a, p. 74, fig.
27.

[non] Ichthyosaurus acutirostris Owen, Fraas, 1891, pl. 8; pl. 11, fig. 1.
[non] Leptopterygius acutirostris (Owen), Hauff, 1953, pl. 19.

Emended Diagnosis

Large ichthyosaurs, length of jaw > 60 cm in mature individuals, fre-
quently > 100 cm; snout relatively long, ratio, length of snout to length
of jaw > 0.62; snout tends to taper to a sharp point; orbit often relatively
large, ratio, diameter of orbit to length of jaw usually not less than 0.18
and may exceed 0.20; sclerotic aperture relatively large, ratio, internal
diameter of sclerotic ring to diameter of orbit frequently > 0.35; maxilla
relatively short, ratio, length of premaxillary segment to length of jaw
> 0.36; ratio, length of external naris to diameter of orbit < 0.60; forefin
with three primary digits and one or two accessory digits; head large
relative to body, especially in larger individuals. Jaw and body length data
approximate more closely to equation, jaw length — 0.1 x (body length)?-?
than to the equation, jaw length — 3.363 x (body length) °-°°” (see remarks
below). Upper Liassic in age, apparently confined to England, probably to
the Whitby locality of Yorkshire.

Holotype

BMNH 14553 (Lydekker, 1889a, p. 73). There is some doubt regarding
the present whereabouts of this specimen (Walker, pers. comm.), and only
an extensive search of the British Museum would confirm whether it has
been lost. At present this is not practical and it will therefore be recorded
that the holotype may be lost.

ae

3
\
See

Ra i

A

aie
4

=

YR

AUS

S

RY

rite)

<t O Q
Fig. 11 Stenopterygius acutirostris (Owen), scale = 40 cm.

A. WMY 5, Upper Lias, Lofthouse, Yorkshire.

B. WMyY 876S, Upper Lias, Kettleness, Yorkshire (photograph laterally inverted).

C. WMyY 8775S, skull, Upper Lias, Whitby, Yorkshire (photograph laterally in-
verted).

BMNH 14533, skull of holotype, Upper Lias, Whitby, Yorkshire (after Owen,
1881, pl. 28, fig. 2).

28

———————

Other Material

WwMyY 5, wMy 2546S, wmy 876S, wmy 878S, YM 497 (complete or near
complete skeletons); wWMy 877S (skull with some post-cranials); WMY
876S(H1), BMNH 1500a (complete skulls) and sMc J35176 (partial skull).

Locality and Horizon

All the material referred to this species is from the Upper Lias, in the
vicinity of Whitby, Yorkshire. Most of the specimens were collected from
the Alum Shales, and also from the Hard Shales and Bituminous Shales
lying above the Jet Rock (see Arkell, 1933, p. 182; Wilson, 1948, p. 28)
in the ammonite zone of Hildoceras bifrons and Dactylioceras commune
[Lower Toarcian].

Emended Description

Because of poor preservation the species is not adequately known, even
though it is represented by at least ten specimens. The holotype is appar-
ently not well preserved.

SKULL

The type skull, figured by Owen (1881, pl. 28, fig. 2) is reproduced in
Fig. 11p (Lydekker, 1889a, p. 74, erroneously refers to Owen’s figure as
pl. 32, fig. 8). Snout frequently sharply pointed, as in WMy 876S, BMNH
1500a, wMy 876S(H1) and wmy 8788S, but decurved appearance figured
by Owen, seen clearly in wMy 8768S, probably an artifact of preservation
because it is not a constant feature. Decurved snouts in BMNH 1500a and
WMY 876S(H1) almost certainly due to dorso-ventral compression, the
thin snout being readily distorted. Snout quite straight in wMy 876S
and wMy 877S, even slightly recurved in wmy 5. Ratio, length of snout
to length of jaw 0.62—0.68 (n= 6), mean value 0.66 (0.62—0.64 in
T. platyodon, n = 3). Measurements taken from Owen’s figure of type
skull give a value of 0.78 for this ratio, but this may be because the snout
was exaggerated in his figure.

Maxilla relatively shorter than in the Temnodontosaurus, indicating a
more advanced stage of cranial evolution (McGowan, 1972b); ratio,
length of premaxillary segment to length of jaw 0.40-0.42 (n= 2),
mean 0.41 (0.30-—0.34 in T. platyodon, mean 0.32, n = 2). Orbital con-
dition similarly more advanced than Temnodontosaurus, ratio, diameter
of orbit to length of jaw 0.16-0.23 (n = 4), mean 0.20 (0.16-0.17 in
T. platyodon, mean 0.17, n=3). Sclerotic aperture variable, ratio, internal
diameter of sclerotic ring to diameter of orbit 0.28—0.40 (n = 4) compared
with 0.24-0.31 (n = 4) in T. platyodon. Ratio, length of external naris
to diameter of orbit (not always a reliable character) relatively small,
0.31-0.57 (n= 4), mean 0.42, compared with 0.53-0.72 mean 0.63
(n = 4) in T. platyodon. Internasal foramen absent (because of poor
preservation this can only be determined in one specimen, sMc J35176,
the holotype of Seeley’s J. zetlandicus).

29

FINS

Fins generally poorly preserved, but are determinate in YM 497, wmy 5,
WMy 877S, wMy 2546S and apparently in holotype. Three primary and
one accessory digits, except in WMY 2546S, which also has one pre-axial
accessory digit. Maximum number of elements in longest digit an estimated
14 in wy 5, 16 in wmy 2546S and 19 or 20 in ym 497. Notching in
radius, radiale and third element in wmy 5S, in radius and radiale in WMY
2546S, only in radius in YM 497, with no notching in wMy 877S. Forefin
not as long and narrow as in T. platyodon, aspect ratio only 2.6 (n = 3)
compared with 3.1 in T. platyodon and 2.3 in S. quadriscissus (mean
values). Relative lengths of fore- and hindfins variable, ratio, length of
forefin to length of hindfin 2.2 in ym 497, 1.2 in wmy 2546S (2.5 in S.
quadriscissus, 1.4 in neotype of T. platyodon).

In wmy 2546S left fore- and hindfins are composites with individual
elements set in plaster in a latipinnate configuration (four primary digits).
Fins on the right side appear authentic and have a longipinnate configura-
tion with three primary digits. Of interest in WMyY 5 is that the humerus has
three distal facets (comparable with Platypterygius, see McGowan, 1972c;
and Ophthalmosaurus, see Andrews, 1910), the smaller of these probably
being for the pisiform. It is not known whether this is a constant feature
of the species. To summarize, the forefin has three primary digits with one
post-axial accessory digit and sometimes one pre-axial accessory. Maxi-
mum number of elements in longest digit up to 20. Notching usually
present.

AXIAL SKELETON AND GIRDLES
Vertebral count to pelvic girdle between 48 and 50 in wmy 2546S, and
approximately 48 in wmy 876S. Vertebral count to tail bend difficult to
determine; in WMY 2546S there is some indication of a disturbance at level
77 and another at level 93, either of which could indicate the position of
the tail bend. In wmy 8768S there is some indication of the bend at about
level 76. It is tentatively concluded that the vertebral count to the tail
bend is approximately 76.

Partial pectoral girdles preserved in WMyY 878S and wmy 5 but comprise
little more than the coracoids. The coracoids are fairly thick and robust and
the pectoral girdle may have been well developed. Anterior notch present.

DENTITION
The teeth are of the usual ichthyosaurian form but appear to be relatively
small (well marked in sMc J35176).

Remarks
1. Reasons for considering S. acutirostris to be distinct from
S. quadriscissus

The only difference between S. acutirostris and S. quadriscissus is size, the
former reaching about three times the size of the latter (based on jaw
length), and it seemed reasonable to conclude that they were part of a

30

continuous growth series of one and the same species. However, the larger
individuals have relatively larger heads than the smaller ones, contrary to
the usual ontogenetic pattern. Allometric growth constants have recently
been evaluated for S. guadriscissus (McGowan, 1973a) and the relation-
ship between the growth of the head relative to the body has been found
to conform to the equation y = 3.363x°°°* (from the allometric growth
equation y = bx® where y = organ size, x = body size, a = the allo-
metric growth constant and b =a second constant). In S. acutirostris,
head growth relative to that of the body conforms to the equation y =
0.1x!-2 but the small sample size (n = 4) does not permit confidence limits
to be set for the estimates of a and b.

Three possible conclusions may be drawn from this:

A. S. quadriscissus and S. acutirostris represent males and females of a
sexually dimorphic species.

B. S. quadriscissus and S. acutirostris belong to a single species in which
changes in allometric growth constants a and b occur during ontogeny.
c. S. quadriscissus and S. acutirostris are distinct species differing in allo-
metric growth constants and maximum attainable sizes.

S. quadriscissus and S. acutirostris occur in separate localities (in Ger-
many and England respectively), which may not be strictly contempora-
neous. Sexual dimorphism may therefore be dismissed.

Abrupt changes in allometric growth constants are uncommon in
ichthyosaurs (McGowan, 1973a), but occur in other animals, usually asso-
ciated with metamorphosis. Martin (1949) found growth in fishes to be
characterized by a series of five stanzas corresponding to four larval stages
and the sexually mature adult. Each stanza had a different set of values
for a and b. In Rana temporaria, the allometric growth constant of the
eye undergoes an abrupt change at metamorphosis (De Jongh, 1967), and
Brown and Davies (1972) working on the cockroach Ectobius, found the
majority of changes in growth constants coincided with metamorphic
changes.

If S. quadriscissus and S. acutirostris were part of a continuous growth
series the abrupt change in allometric growth constants could not be cor-
related with sexual maturity because pregnant females occur in the smaller
form (S. quadriscissus). Maternal specimens are relatively small; 6293
(Stuttgart Museum) has a body length of only 219 cm (See Fraas, 1891,
p. 52, pl. 4, fig. 2) compared with 628 cm in the largest specimen of S.
acutirostris (WMY 2546S). If the two species were part of the same growth
series it would suggest attainment of sexual maturity at an early stage of
growth.

Acquisition of more extensive data from Germany could possibly alter the
position, but for the present it is concluded that S. quadriscissus and S.
acutirostris are separate species.

2. Reasons for synonymizing /. crassimanus, I. longifrons and
I. zetlandicus with S. acutirostris

Blake’s (1876, p. 253) description of J. crassimanus was mainly based on
a large specimen in the York Museum which was redescribed in greater

Sy

detail by Melmore in 1930. The specimen (YM 497), collected from the
Alum Shales north of Whitby, is unfortunately incomplete so that few
measurements can be taken. The anterior portion of the snout is missing
and is reconstructed in plaster, and the body is incomplete beyond the tail
bend. If allowances are made for these missing parts, the head and body
proportions approximate to the growth equation evaluated above for S.
acutirostris. The forefin has three primary and one post-axial accessory
digits, and is consistent with S. acutirostris. The only inconsistency is in the
relative proportions of fore- and hindfins; in wMy 2546S (S. acutirostris)
the ratios, forefin length to hindfin length and forefin width to hindfin width
have values of 1.2 and 1.3, whereas in YM 497, the values are 2.2 and 1.6
respectively. However, the relative size of fore- and hindfin is a variable
character; for example in a sample of 10 specimens of S. quadriscissus the
ratio, forefin length to hindfin length has a range of 2.2—3.1. The aspect
ratio of the forefin is 2.4 in WMy 2546S and 2.9 in ym 497. It is therefore
concluded that there are no major inconsistencies between YM 497 and WMY
2546S and since YM 497 is from the same locality and horizon as S. acuti-
rostris it is referred to that species. J. crassimanus Blake is thus a junior
synonym for S. acutirostris.

In describing J. zetlandicus Seeley wrote, “I am acquainted with no other
ichthyosaur in which the skull attains this broad, triangular form, with the
orbits so far apart from each other and so moderately inclined, and with the
nares so far in front of the orbits and relatively so large . . . These characters
sufficiently distinguish the species from all others.” (Seeley, 1880, p. 646).
The holotype (smc J35176), a large incomplete skull from the Upper Lias
of Whitby, is preserved in-the-round and the absence of distortion gives a
very broad appearance when viewed from above. However, compared with
other in-the-round skulls (BMNH R8177, BMNH 49203, both J. communis),
SMC J35176 is no broader nor are the orbits any further apart. Because the
skull is incomplete few comparisons can be made, but the ratio, length of
external naris to the diameter of orbit is larger (0.57) than it is in S. acuti-
rostris. However, the sample size is small (n = 3), and this character is known
to be variable (for example in Stenopterygius quadriscissus the observed
range is 0.25—0.45, n = 9). Furthermore the holotype of J. zetlandicus 1s
from the same locality and horizon as S. acutirostris. I. zetlandicus is there-
fore concluded to be a junior synonym for S. acutirostris.

Owen’s description of J. longifrons comprised a brief reference to some
figures (1881, pls. 23-27). The skull figured is identified by Lydekker as
BMNH 33157, from the Upper Lias of Curcy (1889a, p. 78). Lydekker noted
that, “In all essential characters this specimen agrees with the preceding [a
cast of the holotype of J. zetlandicus] . . .” Lydekker synonymised J. longi-
frons with (the now invalid) I. zetlandicus, a course taken by most authors
(see Woodward and Sherborn, 1890). Only one character can be measured
in BMNH 33157, the ratio, length of external naris to diameter of orbit (0.38)
which lies within the observed ranges for S. acutirostris (0.31-0.57).
I. longifrons is thus concluded to be a junior synonym of S. acutirostris.

IZ

3. Reasons for rejecting /. latifrons Koenig as a nomen dubium

I. latifrons was first mentioned by Koenig who figured an incomplete skull
and partial vertebral column (1825, pl. 19, fig. 250) and most authorities
consider this sufficient to make the name available (Woodward and Sher-
born, 1890; Lydekker, 1889a, Kuhn, 1934). The figure was not accom-
panied by a written description, and the specimen (BMNH R1122) is quite
indeterminate. Owen figured the skull (1881, pl. 27, fig. 1) and Lydekker
noted that it was probably collected from the Lower Lias of Barrow-on-Soar,
Leicestershire (1889a, p. 90, fig. 33). Because the holotype is indeterminate
it is not possible to compare it with any other material. The name /. latifrons
is thus not applicable to any known taxon and is accordingly rejected as a
nomen dubium.

a3

Conclusion

Of the five species of longipinnate ichthyosaurs of the English Lower Jurassic
three are from the Lower Lias: Temnodontosaurus platyodon (Conybeare),
T. risor, sp. nov., and T. eurycephalus, sp. nov. T. longirostris (Mantell)
extends from Lower to Upper Lias, while Stenopterygius acutirostris (Owen)
is confined to the Upper Lias. T. platyodon and S. acutirostris are both large,
the former reaching a total length of 9 m, the latter approaching 8 m. Body
length cannot be estimated for T. eurycephalus, but as the skull is in excess
of 1 m, the species is assumed to have been comparable in size to T. platyodon
and S. acutirostris. T. risor and T. longirostris were probably both of more
moderate size, and much smaller than either 7. platyodon or S. acutirostris.

T. eurycephalus, with its short snout and massive skull, and 7. longi-
rostris, with its long and delicate snout were the most highly specialized
species. It was suggested above that 7. eurycephalus may have fed upon other
ichthyosaurs, and the short deep skull and heavy teeth are certainly sug-
gestive of a voracious predator. On the other hand, 7. longirostris, with its
long thin snout, probably fed exclusively on small fishes.

S. acutirostris differs from its German contemporary S. quadriscissus in
being larger and having a relatively larger head. Indeed the two species are
so similar that they might well have evolved from similar stocks by way of a
change in the allometric growth constants of the head and body.

Acknowledgments

I wish to express my sincere thanks for the help and hospitality I received
from the staffs of the many institutions visited. I particularly wish to thank
Dr. Alan Charig, Mr. Cyril Walker, Mr. Phillip Palmer, and Miss A. L.
Holloway of the British Museum (Natural History); Dr. Colin Forbes of the
Sedgwick Museum and Mr. Peter Biddlestone, formerly of the Sedgwick
Museum, Cambridge, now of the Royal Ontario Museum; Mr. Phillip Powell
of the Oxford University Museum; Mr. Allen Butterworth and Ms. Barbara
Pyrah of the Yorkshire Museum; Mr. J. G. Graham of the Whitby Museum,
Yorkshire; Dr. J. E. Hemingway of the University of Newcastle-upon-Tyne;
Dr. Paul McGrew of the University of Wyoming; Mr. Andrew Mathieson
and Mr. M. J. Jones of the Leicester County Museum, and the staff of the
Clarks Shoe Museum, Street, Somerset.

I thank Mrs. Janet Clarke and Mrs. Lynda Spicer, ROM, for their secre-
tarial help; Mrs. Sophie Poray, RoM, for the drawings; Mr. Leighton Warren
and Mr. Alan McColl, Photography Department, rom, for photographs;
and Miss E. Dowie of the Ro library for assistance with literature searches.
For reading the manuscript and making many helpful suggestions I thank
Dr. Allan Baker, Department of Ornithology, ROM and Dr. Gordon Edmund,
Department of Palaeontology, ROM.

34

Literature Cited

ANDREWS, C. W.
1910 A descriptive catalogue of the marine reptiles of the Oxford Clay based

on the Leeds Collection in the British Museum (Natural History), London.

Part 1. London, Printed by order of the Trustees of the British Museum.

205 pp.

ARKELL, W. J.
1933. The Jurassic system in Great Britain. Oxford, Clarendon Press. 681 pp.

BLAKE. J. F.
1876 Order Ichthyopterygia. In Tate, R. and J. F. Blake. The Yorkshire Lias.
London, J. Van Voorst, pp. 246-261.

BROWN, V. AND R. G. DAVIES
1972 Allometric growth in two species of Ectobius (Dictyoptera: Blattidae).
Proc. Zool., vol. 166, pt. 1, pp. 97-132.

CONYBEARE, W. D.
1822 Additional notices on the fossil genera Ichthyosaurus and Plesiosaurus.
Trans. Geol. Soc. Lond., ser. 2, vol. 1, no. 1, pp. 103-123.
DE JONGH, H. J.
1967 Relative growth of the eye in larval and metamorphosing Rana temporaria.
Growth, vol. 31, pp. 93-103.

DEAN, W. T., D. T. DONOVAN AND M. K. HOWARTH
1961 The Liassic ammonite zones and subzones of the North-Western European
Province. Bull. Br. Mus. Nat. Hist., Geol., vol. 4, no. 10, pp. 435-505.

DE LA BECHE, H. T.
1822 Remarks on the geology of the south coast of England, from Bridport Har-
bour, Dorset, to Babbacome Bay, Devon. Trans. Geol. Soc. Lond., ser. 2,
vol. 1, pp. 40-47.
1826 On the Lias of the coast, in the vicinity of Lyme Regis, Dorset. Trans. Geol.
Soc: Lond. ser. 2, vol: 2, no; 1, pp; 21-30.

DE LA BECHE, H. T. AND W. D. CONYBEARE
1821 Notice of the discovery of a new fossil animal, forming a link between the
Ichthyosaurus and the crocodile, together with general remarks on the
osteology of the Jchthyosaurus. Trans. Geol. Soc. Lond., ser. 1, vol. 5,
no. 2, pp. 559-594.

DELAIR, J. B.
1960 The Mesozoic reptiles of Dorset (Part m1: conclusion). Proc. Dorset Nat.
Hist. Archaeol. Soc., vol. 81, pp. 59-85.
1969 A history of the early discoveries of Liassic ichthyosaurs in Dorset and
Somerset (1779-1835) and the first record of the occurrences of Ichthy-
osaurs in the Purbeck. Proc. Dorset Nat. Hist. Archaeol. Soc., vol. 90,

pp. lo=132:
FRAAS, O.
1891 Die Ichthyosaurier der Suddeutschen Trias- und Jura-Ablagerungen. Tiibin-
gen. 81 pp.
HAUFF, B.
1953. Das Holzmadenbuch, Ohringen, Verlag der Hohenlohe’schen Buchlandlung.
54 pp.

3D

HAWKINS, T.
1834 Memoirs of Ichthyosauri and Plesiosauri, extinct monsters of the ancient
earth. London, Rolfe and Fletcher. 58 pp.
1840 The book of the great sea-dragons, Ichthyosauri and Plesiosauri, .. .
gedolim taninim, of Moses. Extinct monsters of the ancient earth. London,
W. Pickering. 27 pp.

HEMINGWAY, J. E., V. WILSON AND C. W. WRIGHT
1968 Geology of the Yorkshire Coast. Geologists’ Association guides no. 34,
Rev. ed. Colchester, Benham. 47 pp.

HUENE, F. VON
1922 Die Ichthyosaurier des Lias und ihre Zusammenhange. Monogrn. Geol.
Palaont., ser. 1, heft 1, pp. 1-114.
1948 Short review of the lower tetrapods. Jn Du Toit A.L., ed. Robert Broom
commemorative volume. Royal Society of South Africa special publication.
Capetown, Published by the Society, pp. 65-106.

JAEKEL, O.
1904 Eine neue Darstellung von Ichthyosaurus. Z. Dt. Geol. Ges., vol. 56,
pp. 26-34.
JAGER, G.

1856 Uber eine neue Species von Ichthyosauren (Jchthyosaurus longirostris
Owen et Jager). Nebst Bemerkungen uber die ubrigen in der Liasformation
Wurttembergs auf gefunden Reptilien. Nova Acta Acad. Caesar. Carol.,
vol. 25, pt. 2, pp. 939-967.

KOENIG, E. C.
1825 Icones Fossilum Sectiles. Centuria Prima. London. 4 pp.

KUHN, O.
1934 Ichthyosauria. 7m Quenstedt, W., ed. Fossilium Catalogus. 1: Animalia.
Pars 63. Berlin, Junk, pp. 1-75.

LYDEKKER, R.

1889a Catalogue of the fossil Reptilia and Amphibia in the British Museum
(Natural History). Part um. Containing the orders Ichthyopterygia and
Sauropterygia. London, Printed by Order of the Trustees of the British
Museum. 307 pp.

1889b Palaeozoology; Vertebrata. Jn Nicholson, H. A. and R. Lydekker. A manual
of palaeontology for the use of students with a general introduction on the
principles of palaeontology. 3d. ed. vol. 2, part 3. Edinburgh, W. Black-
wood, pp. 889-1474.

MANTELL, G. A.
1851 Petrifactions and their teachings; or, a hand-book to the gallery of organic
remains of the British Museum. London, H. G. Bohn. 496 pp.

MARTIN, W. R.
1949 The mechanics of environmental control of body form in fishes. Univ.
Toronto Stud. Biol. Ser., no. 58, pp. 1-91.

MCGOWAN, C.
1969 The cranial morphology and interrelationships of the Lower Liassic
ichthyosaurs. Ph.D. thesis, University of London. 498 pp.
1972a The distinction between latipinnate and longipinnate ichthyosaurs. Life Sci.
Occ. Pap., R. Ont. Mus., no. 20, pp. 1-12.

36

1972b Evolutionary trends in longipinnate ichthyosaurs with particular reference
to the skull and fore fin. Life Sci. Contr., R. Ont. Mus., no. 83, pp. 1-38.

1972c The systematics of Cretaceous ichthyosaurs with particular reference to the
material from North America. Contr. Geol. vol. 11, no. 1, pp. 9-29.

1973a Differential growth in three ichthyosaurs: Ichthyosaurus communis, I.
breviceps and Stenopterygius quadriscissus (Reptilia, Ichthyosauria). Life
Sci. Contr., R. Ont. Mus., no. 93, pp. 1-24.

1973b The cranial morphology of the Lower Liassic latipinnate ichthyosaurs of
England. Bull. Br. Mus. Nat. Hist., Geol., vol. 24, no. 1, pp. 1-109.

In Press A revision of the latipinnate ichthyosaurs of the Lower Jurassic of England

(Reptilia: Ichthyosauria). Life Sci. Contr., R. Ont. Mus.

MELMORE, S.
1930 A description of the type-specimen of Jchthyosaurus crassimanus, Blake
(Owen MS). Ann. Mag. Nat. Hist., ser. 10, vol. 6, pp. 615-619.

OWEN, R.
1840 Report on the British fossil reptiles. Part 1. Rep. Br. Ass. Advmt. Sci.,
vol. 9, pp. 43-126.
1881 A monograph of the fossil Reptilia of the Liassic formations. Part m1. Plesi-
osaurus, Dimorphodon, and Ichthyosaurus. [Part 11] Order Ichthyopterygia
...Ichthyosaurus. Palaeontogr. Soc. [Monog.] 35, pp. 83-134.

PHILLIPS, J.
1875 _ Illustrations of the geology of Yorkshire; or, a description of the strata and
organic remains. Part 1. The Yorkshire Coast. 3d. ed. Edited by R. Ether-
idge. London, J. Murray. 354 pp.

QUENSTEDT, F. A.
1858 Der Jura. Tubingen, H. Laupp’sche buchhandlung. 842 pp.

SEELEY, H. G.
1880 On the skull of an Ichthyosaurus from the Lias of Whitby, apparently in-
dicating a new species (J. zetlandicus, Seeley), preserved in the Woodward-
ian Museum of the University of Cambridge. Q. J. Geol. Soc. Lond., vol. 36,
pp. 635-647.

WILSON, V.
1948 _— British regional geology; East Yorkshire and Lincolnshire. London, His
Majesty’s Stationery Office. 94 pp.

WOODWARD, A. S. AND C. D. SHERBORN
1890 A catalogue of British fossil Vertebrata. London, Dulau. 396 pp.

WOODWARD, H. B. AND W. A. E. USSHER

1911 The geology of the country near Sidmouth and Lyme Regis. 2d. ed. Mem.
Geol. Surv. Engl. Wales. Sheet (B), nos. 326, 340, pp. 1-102.

ay.

At

ISBN 0-88854-151-1